Thorium-silicon-beryllium alloys



Feb. 10, 1959 F. G. FOOTE 2,

THORIUMASILICON-BERYLLIUM ALLOYS Filed June 9, 1948 IN VENTOR.

7 Frank Foote United States Patent 6 THORIUM-SILICON-BERYLLIUM ALLOYS Frank G. Foote, Plandome, N. Y., assignor to the-United-- States of America as represented by the United States Atomic Energy Commission This invention relates to alloys of thorium and-more particularly to alloys wherein thorium metal is alloyed with more than one other element.

An-object of this invention is to provide an alloy of thorium having improved physical properties, namely, increased resistance to corrosion and improved hardness values.

A further object of this invention is to provide an alloy of thorium containing certain added'elements to impart special properties to the thorium metal wherein these special properties are increased to a degree beyond that ordinarily expected to result from the addition of equal or even greater amounts of either of-theminor alloying elements alone.

Other objects and advantages-will be" apparent 'to' those skilled in the art upon further examination of this'specification and the accompanying drawing 'which is the thorium corner of the phase diagram. for the ternary system'comprising thorium, siliconand beryllium;

In accordance with this invention, it has'been dis-'.' covered that the simultaneous use of both silicon and beryllium as alloying elements with thorium produces an. alloy having physicalproperties at'least comparable or even superior to those found in the binarythorium alloys containing either beryllium or silicon alone. Moreover, it appears that the simultaneous use of both silicon and beryllium in a thorium alloy produces a synergistic effect in that the sum of the amounts of both silicon and beryllium used in combination with each other is less than the amount of either of the alloying elements used singly to produce a thorium alloy having. identical or improved properties.

The ternary alloysof thorium, silicon and b'eryllium show increased hardness values and a greater resistance to aqueous corrosion 'than' is found in'pure thorium metal or in either binary alloy consisting of thorium-silicon or thorium-beryllium. On account of these improved physical propertiesand because oftheir characteristics suitable for nuclear bombardment processes, these ternary alloys are well adapted for use in construction of watercooled chain-reacting piles.

The subject matter of this invention includes those ternary alloys consisting primarily of thorium metal is 4.5 and the balance is substantially" pure thorium.

Such alloys have improved physical characteristics over those found in thoriummetal or eithe'r' of 'the binary alloys of thorium containingsilicon-or beryllium'alone. These limits for compositions of matter within the purview ofthis invention are heavy solidlines.

Upon further investigation of the thorium corner of the phase diagram for the three-component system, it has been discovered thatthoriumalloyed with between 0.4 and-3.0% by weight beryllium and'between 0.3 and 3.0% by weight silicon wherein the total weight percent of minor alloying elementsis between 1.5and 4.0% by weight constitutes a preferredrange for each of the elements present. The' limits of the preferred compositions of matter are designated by the broken lines and the solid line joining the broken lines for compositions containing 1.5% total beryllium and silicon. Stated in terms of percent of thorium, such total Weight percents of minor alloying elements necessarily implies alloys containing between 96.0 to 98.5 weight percent thorium. These alloys containing thorium, silicon and beryllium within the-above ranges show increased hardness values as follows:

whereas an alloy having a composition outside the preferred'area, e. g. 0.64 and 0.44'weight percent for silicon andberylliumrespectively, shows a cast hardness of only 69 on the Rockwell B scale.

Increasedresistance to aqueous corrosion as Well as improved hardness values is shown by those ternary compositions consisting of thorium metal alloyed with between 1.0 and 1.5% by weight beryllium and between 0.5 and 1.0% by weight silicon wherein the total weight per-cent of said minor alloying elements is between 1.5 and 2.0% byweight.

The following tabulated data demonstrate the superior resistance to corrosion and hardness found in the ternary alloys in comparison to the binary thorium-silicon and thoriumberyllium alloys.

TABLE I Corrosion of thorium alloys in water (178 C.)

(autoclave tests) Cast Hard- Weight Change (mg/cm!) Based on Uncleaned Specimens Nominal W t. Percent Alloy ness Values 7 Element onRockwell 5" Scale 0.8 day 1.7 days 4 days 8 days 16 days 32 days Thorium 52 0. 47 0. 00 -0. 04 12. 3 -94. 3 348 Til-14.08 wt. Percent Si.-- 68 0.51 0. 69 1.0 39. 2 -171 -495 Th+2 wt. Percent 75 0. 20 0.26 1.0 -9. 3 106 339 Th+4.3 wt. Percent Si 88 0.0 -0. 28 0.03 -12. 3 74 -249 :38:32 gt; s9 -0. 5s -1. 0 -o. as -0. s3 -3. a +0. 4 Th+b.4 wt: Percent Be 84 0. 4a 1. 7 1. 65 5. 0 7. 0 +28 Th+0.94 wt. Percent Be 68 0.32 -0. 13 Th+2.46 Wt. Percent Be 87 -0. 1. 2 1. 1 -0. 97 -0. 6 -0. 7

I Completely corroded.

shown in the drawing bythe TABLE 11 Corrosion rates of pure Th, Th-exploratory alloy binary systems, and Th-Si-Be ternary in boiling distilled 11 I Cast Hard- Welght Percent of Alloy Heat Treatment ness on Hours of Wt. Change, Material Rockwell Test mg./cm.=/hr.

B" Scale Pure Thorium Extruded 52 852 003 0.42 Beryllium-.. Cast from 1,355 O... 84 112 005 0.94 Beryllium..- Cast from 1,350" C... 68 112 008 1.6 Berlylllum.. Cast (BeO cruclble).. 68 112 0023 Cast from 1,330 O..- 87 112 003 1. Cast from 1,755 C--. 68 112 -l-. 002 2.0 Cast from 1,660 O--- 75 112 002 4.3 Silicon Cast from 1,670 O... 88 112 002 0.62 Silicon; 1.11 Beryllium- Cast from 1,330" O... 89 11? 001 The thorium-silicon eutectic occurs at approximately 2% by weight silicon and melts above 1300 C. whereas the eutectic for the binary thorium-beryllium alloy occurs at approximately 2% by weight beryllium and melts between 1100 and 1200 C. The two eutectics are connected by an eutectic valley sloping from a maximum at the thorium-silicon eutectic to a minimum at or very close to the thorium-beryllium eutectic.

By examination of the microstructures of the alloys defined by the subject matter of this invention it appears that the ternary alloys consisting of thorium, beryllium and silicon are, in reality, mixtures of the binary eutectics. Samples of these binary and ternary alloys were etched electrolytically in phosphoric acid solution prior to examination of the microstructures.

The binary-thorium-silicon eutectic occurring at 2% by weight silicon appears as a coarse eutectic made up of gray particles. The binary thorium-beryllium eutectic, also containing about 2% by weight of the minor alloying element, beryllium, appears as an extremely fine herringbone type upon examination of the microstructure.

The ternary eutectic does not'have an easily recognized microstructure and the ternary alloys in the vicinity of the eutectic valley show these binary eutectics as they appear in the binary alloys, neither altering the appearance of the other.

For example, the ternary alloy, wherein 1.05% by weight beryllium and 1.64% by weight silicon is alloyed with thorium, appears to consist primarily of a coarse silicon eutectic mixed with a small amount of the extremely fine beryllium eutectic. Where thorium is alloyed with 1.11% by weight beryllium and 0.62% by weight silicon, the microstructure reveals large amounts of both the coarse-grained silicon-thorium eutectic and the fine herringbone type beryllium eutectic, and in this structure the quantitative relationship between the two types of eutectic mixtures was not quite so marked.

It will be apparent to those skilled in the art to which this invention pertains that various modifications may be made Without departing from the principles of the invention as disclosed herein, and thus it is not intended that the invention should be limited other than by the scope of the appended claims.

What is claimed is:

1. An alloy consisting essentially of thoruim, silicon and beryllium.

2. An alloy consisting essentially of thorium as the predominant ingredient and minor quantities of silicon and beryllium.

3. An alloy consisting of thorium, silicon and beryllium wherein beryllium and silicon are each present in amounts between 0.1 and 3.5% by weight and the total weight percent of said minor alloying elements is between 1.5 and 4.5, and the balance is substantially thorium.

4. An alloy consisting of thorium, silicon and beryllium wherein the beryllium present is between 0.4 and 3% by weight and the silicon present is between 0.3 and 3.0% by weight, and the total weight percent of said minor alloying elements is between 1.5 and-4.0.

5. An alloy consisting of thorium, silicon and beryllium wherein the hardness values range upwards from on the Rockwell B scale and there is improved resistance to corrosion in the cast alloy containing beryllium between 10 and 1.5% by weight and silicon between 0.5 and 1.0% by weight, and the total weight percent of said minor alloying elements is between 1.5 and 2.0% and the remainder is predominantly thorium.

Power, p. 364 (1947), publ. by Addison-Wesley Press, Cambridge, Mass. 

1. AN ALLOY CONSISTING ESSENTIALLY OF THORIUM, SILICON AND BERYLLIUM. 